1. Field of the Invention
The present invention relates to a phantom power circuit included in a condenser microphone, more specifically a phantom power circuit automatically limiting the output of a pulse current generated in association with connection or disconnection of a condenser microphone.
2. Related Background Art
Power supply systems for condenser microphones and other microphones are set forth in the EIAJ standard (RC-8162A). The EIAJ standard, which pertains to a phantom power source, defines three types of supply voltages (12 V, 24 V, and 48V).
The phantom power source is a DC power supply. To supply power, a DC voltage is applied to input terminals (HOT terminal and COLD terminal) of a condenser microphone through supply resistors. The voltage of the same level is applied to the HOT terminal and the COLD terminal. Unless the both terminals (HOT terminal and COLD terminal) of the condenser microphone are connected or disconnected simultaneously to and from the phantom power source, a rush current, which is a pulse-shaped current, occurs even if it is momentarily.
With generation of such a pulse current, sound associated with the pulse current is output to an output device connected through the phantom power source for outputting sound input from the condenser microphone. The output sound resembles an impact sound. Such output sound after being amplified through an amplifier generates a loud and uncomfortable popping sound, which may also damage the output device.
Such a pulse current is not generated if the condenser microphone and the phantom power source are connected or disconnected in a state where the switch of the condenser microphone or the switch of the phantom power source is turned off. In the actual use, however, the condenser microphone and the phantom power source are connected or disconnected without switching off, in order to enhance work efficiency. Under the circumstances, a phantom power source is demanded that automatically limits the output of a pulse current and operates in a normal mode with no pulse current generated.
Although no related art literature has been found intended to automatically limit the output of a pulse current associated with connection or disconnection of a condenser microphone in a phantom power circuit, Japanese Unexamined Patent Application Publication No. 2009-290639 discloses technology pertaining to the present invention.
The invention disclosed in Japanese Unexamined Patent Application Publication No. 2009-290639 is directed to a method of connecting a tubular body that can be used as a connector housing of a condenser microphone unit. A zener diode element for blocking overcurrent is provided on a circuit board accommodated in the connector housing.